Variable reluctance amplifier



Aus. 1o, 1954 F. s. MACKLEM A2,686,292

VARIABLE RELUCTANCE AMPLIFIER 2 Sheets-Sheet 1 Filed uarch 92 1951 ro24' Heaters Illu...

F. SUN/ERLAND MAC/(LEM Bg rw Aug. l0, 1954 F. s. MACKLEM VARIABLERELUCTANCE AMPLIFIER Filed March 9, 1951 2 Sheets-Sheet 2 "i fe LL S I..HH] l Snventor w rw Gttornegs Patented Aug. 10, 1954 UNITED STATESPATENT OFFICE VARIABLE EELUCTANCE AMPLIFIER F. Sutherland Maclilem 21Claims. l

My invention relates to devices variously known as saturable reactors,transductors, and magnetic amplifiers for the control of A.-C. power andis the nature of an improvement over the circl 'ts disclosed in mycopending patent applications Serial No. 138,094, iiled January 12,1950, and Serial No. 149,235, led March 13, 1950.

In the prior art, control of A.- C. power has been accomplished by meansof electronic ainpliers or magnetic amplifiers. Electronic amplifiershave the disadvantage that they require associated D.C. power supplieswhich are relatively bulky and expensive to construct. Magneticamplifiers have the disadvantage that they rely upon saturation of aferro-magnetic core material and therefore are inherently highlynonlinear devices. ln particular, they tend to deliver a highlydistorted waveform to their load when excited with a sinusoidal input.In addition, the inherent non-linearity of magnetic ampliiiers makesthem extremely difficult to design for optimum performance. Furthermore,magnetic ampliers introduce relatively long time delays which in someapplications are very serious.

lt is, accordingly, an object of the to provide an improved device ofthe indicated.

Zit is another object to provide an improved means for controlling thepower delivered to a two-phase load.

It is also an object to provide improved means for differentiallyresolving two independently variable signals.

it is a further object to provide an improved me. ns for deriving, fromtwo input signals (one variable independently of the other), an outputsignal of phase and magnitude reflecting the instantaneous relativedifference between the input signals.

lt is still another object to provide a two-phase variable reluctancecontrol device with means for ng substantially constant auxiliaryvoltages therefrom, more or less regardless of the controlled operationthereof.

It is specific object to meet the above ohjects 'with an improvedmagnetic-control device which may not depend upon magnetic saturation orany ci the phenomena associated with saturation.

It is another specific object to meet the above objects with'variable-reluctance devices substantially less susceptible Ytomagnetic-shunt paths and other spurious effects.

t is a further speciiic object to provide a servo amplifierincorporating improved selectable errorrate-danping characteristics.

invention character Freeport, N. Y., assigner to Servo Corporation ofAmerica, New Hyde Park, N. Y., a corporation of New York Applicationlliarch 9, 1951, Serial No. 214,696

Other objects and various further features of novelty and invention willbe pointed out or will occur tc those skilled in the art from a readingof the following speciiication, in conjunction with the accompanyingdrawings. In said drawings, which show, for illustrative purposes only,preicrred forms of the invention:

Fig. 1 is a siniplied circuit diagram showing a control device accordingto the invention` Fig. 2 is a diagram oi a modification oi lrig. 1; and

3 is a further circuill diagram illustrating another inodication.

Briefly stated, my invention contemplates means for controlling A.-C.power transferred magnetically from primary-winding means tosecondary-winding means oy introducing a variable reluctance in serieswith the magnetic path between the primary and the secondary. Theinvention utilizes magnetic-core means comprising two flux-loop paths,and at least a portion of each iiuX-loop path is independent of theother. Primary, secondary, and tertiary windings may he coupled to theindependent portions of each fluxloop path; and, hy interconnecting theprimary windings in a sense opposed to interconnection of the secondarywindings, a load across the secondary windings may be energized with achanging phase and magnitude reflecting changes in control impedanceacross a tertiary winding. In one form, the core means may be ofthree-legged coniguration, with the center leg comLion to the twolinx-loop paths, the windings being coupled to parts of the coreexternal to the cc non leg; in another form, two completely inde ntcore-s may be employed. Whatever the core coniguraton, I show howfurther windings may he coupled to the two linx-loop paths and connectedto each other to produce an essentially constant auxiliary-supplyvoltage, as f and E-plns supply, more or less changes in controlimpedance and, thereiore, more or less regardless of changes in theproportional distribution oi iiux in the two flux-loop paths. I alsoshow how a variable-reluctance con.-

trol means ci the character indicated may Toe utilized as aservo-amplifier, with selectable errorrate damping characteristicsincorporated therein.

Referring to the schematic arrangement oi Fig. l, I show invention inapplication to a means for controlling the magnitude and phase of powerdelivered to a two-phase load 5, which may loe a reversible motor drivenin one direction at Varying speeds in accordance with varying resultantvoltages of one phase induced in secondary windings t-l the motor may bedriven in the opposite direction at varying speeds in accordance withresultant voltages of opposite phase induced in the windings t-. Toproduce these results, the secondary windings -'l may be independentlycoupled to independent parts oi two flux-loop paths, as dened bymagnetic-core means of appropriate configuration.

In the form shown in Fig. 1, the magnetic-core means is a singleelement, as of the type disclosed in the above-mentioned copendingapplications. This element may include three legs-an outer leg 3, amiddle leg S, and another outer leg l5. The center' leg 9 may be commonto two uX-loop paths, deiining ilux circulations 4u and fpz independentof each other, except in the center leg $5, where the flows may be inthe Same direction. To establish such independent flux circulations, asingle primary coil may be coupled to the center leg e and energized bya source l I of alternating current; however, in the form shown, Iemploy two like primary windings lZ-l independently coupled to the twoflux-loop paths at locations external to the common portion 9 of thesepaths. In order that the secondary output appearing across the load 5may reflect the diierence or resultant of iiuxes qhi and c2, the primarywindings may be so wound and connected to each other, with respect tothe sense of winding and of interconnection of the secondary windings 67, that the primary connections are effectively the reverse or oppositeof the secondary connections. In the form shown, both primary windings12-13 advance in the same sense and are connected in series, while bothsecondary windings 6-1 advance in the same sense but are connected inopposition across the load 5.

It will be appreciated that with the same number of primary turns l2linked to the left-hand flux loop S-Q as the number of primary 'turns i3linked to the other ux loop Q-lc, and in the absence of conditionsproducing asymmetry of ilux distribution, a given source excitation (ill will cause iluXes gbr and qz to circulate with uniform magnitude andphase in their respective paths. Likewise, it will be understood that,if the number of turns in secondary winding t equal the number of turnsin secondary winding l', then the voltages induced in these windingswill be of equal magnitude and opposite phase, so that no resultantvoltage will be applied to the load 5, and the load 5 (in the case of amotor) will not operate.

As explained in the said copending application Serial No. 149,235, themotor 5 may be controlled by variable-reluctance means incorporated inone of the flux-loop paths, but, in the form shown, I employ suchvariablereluctance means in conjunction with both flux-loop paths.Variable-reluctance control may be elected by Variabledmpedance meanssuch as a space-discharge device it connected across a tertiary windingl5 linked to an independent part, such as the leg 8, of one of thefluxdcop paths; with a similar construction for the other flux-looppath, a space-discharge device l5 may be connected across anothertertiary winding il', coupled to the independent leg 4 manner, foracceptance of control signals to be utilized in the differentialenergizing of the motor With the described arrangement, it will beappreciated that, if an input signal at 2@ predominates over an inputsignal at El, the tertiary winding i5 will restrict the flow of flux dicompared with ow or flux d2, so that the secondary voltage induced atthe winding 'l may predominate over that induced at E; the phase of thevoltage induced at l will be displaced with respect to the phase oi thevoltage induced at t, so that the motor 5 will be energized inaccordance with the diierence between or resultant of these inducedvoltages. Likewise, should the input at 2l predominate over the input at2t, the reverse condition will apply, and the motor will be driven inthe reverse direction.

It will be appreciated that the described con struction is characterizedby arrangement of the primary, secondary, and tertiary windings inrelative proximity to each other and on the independent parts of each ofthe two flux-loop paths. Such construction assures that all ilux (p1generated in the core upon energizing primary coil i2 will be linked tothe secondary and tertiary coils S and i5, and that all iiux es due toenergizing primary coil I3 will be linked to the secondary and tertiarycoils L -ll, regardless or" magnetic-shunt eiects, as occasioned byaccidental proximity of other ferro-magnetic materials to the core. Thepresence or" such shunts will have substantially no eiect upon theseparate flux-linkage relationships of the primary, secondary, andtertiary coils on the respective independent sides oi the coniiguration.

As a further feature oi the invention, I provide a means for utilizingthe iluXes n-qbz, regardless of their relative magnitudes, in thegeneration of substantially constant auxiliary-supply voltages, as forexample a heater supply and a B-plus supply. Constant heater voltage maybe derive-d from two auxiliary coils 2S-2li, each having the same numberof turns and connected in series, and each independently linked orcoupled to the independent branches S--lil of the two ilus;- loopp-aths. In a similar manner, two auxiliary coils 25-25 may be connectedin series and coupled to the independent legs S-l c for generation of asubstantially constant B-plus supply. It will be seen that, since aconstant source voltage at il may produce a constant total iluX(dn-tez), the total induced voltage in windings ZB-t (or in windings25-26) may be substantially constant, regardless of the control effectedby the space-discharge means lil-4t.

In Fig. 2, I show an alternative arrangement which ina-y lend itseli tomore ready packaging, in that for a given power capacity or thevariablereluctance control means, the magnetic-core means need not be sobulky in a given projection. To illustrate the functioning of thisbetterpackaged construction, the magnetic-core means 2'1-23 of Fig. 2 isspread out, but it will be understood that the construction lends itselfto a folded arrangement wherein the core means 2l and the core means 28may be virtually sanda wiched. In the arrangement of Fig. 2, the twoflux-loop paths are completely independent and are dened by twoindependent cores 2li-2S. In view of the similarity of electricconnection for the arrangement of Fig. 2 as compared with thearrangement or Fig. 1, functionally similar elements have beendesignated with the same reference numerals primed; thus, the source Ilis applied across two like primary coils |2'-i3, each linked toindependent portions of the two i'luxloop paths. 'Ihe secondary coils6--'I are similarly linked to independent portions of the loop paths,and the primary windings and the idary wind'figs are so wound andinterconnected as to produce Vacross the load 5 a resultant veren-acting the instantaneous difference in i ilui; in the two paths ofcores Ell- 28. For che-.ratio purposes, l show a first variablereistance a second variable resistance 3! connected across therespective tertiary windings for eiiecting the desired control of themotor 5. As before, suitable interconnection of windings 23'-t and 25'-2may provide substantially constant heater B-plus and other supplies forauxiliary purposes.

As indicated generally above, it is a feature of the invention that myimproved variable-reluctance control means may incorporate error-ratedamping, with selectable characteristics for appropriate control in aservomechanism. I show such an arrangement in Fig. 3, wherein I employ avariable-reluctance device of the type shown in Fig. 2. In Fig. 3,fluxes o1 and o2 are circulated two magnetic cores 35-35, constitutingindependent fluxuloop paths. Primary windings iii-3S are so wound andinterconnected that, when energized the source 3%, the fluxes o, and o2flow in opposite directions around the paths of core means 3ro-3&3.Secondary windings titlili may also be linked to the paths andinterconnected to apply a resultant of their induced voltages across aload 42, which again may be a reversible two-phase motor. For controlpurposes, a rst space-discharge means i3 may be connected in push-pullacross tertiary winding 14, linked to the flux loop path of core 35; andin like manner, the space-discharge device 65 may be connected to asecond tertiary winding 46.

In the orm shown, the inputs to the spacedischarge devices :t3-i5 areinterconnected but with opposite phase, as by the lines lil, and theseinputs are balanced with respect to ground on the secondary side or" a-ninput transformer 53. Positive-biasing means, at the connection 4B, maybe applied via suitable resistors Sil-5| to the space-discharge means4.3-45, as at the cathode circuits thereof, so as to bias both dischargedevices iZ'B-l below cut-off in the normal situation in which iluxes(p1, o, circulate in their respective paths with the same magnitude andphase. Upon application or" a given control signal at the input d8, oneof the space-discharge devices t-d5 will be driven to saturation so assubstann tiall'y7 to restrict the flow of flux in the path controlledthereby. Should this happen to the discharge device the flow of flux c,in the core 35 will substantially increase in relation to the iiux o2,and a substantial secondary voltage will be generated across thesecondary winding 40; this voltage will predominate over the secondaryvoltage at di, and the motor :l2 will be driven accordingly.

In accordance with the invention, I utilize this substantial increase influx (or) to generate a feedback signal 1"' or immediate application asadditional bias on the then-saturated space-discharge device (it). Suchfeedback or bias means may take numerous iorms, but in the presentarrangement I derive the necessary voltage directly from the secondarywinding lill, as by employment of a rectier, such as the diode 52, andsuitable smoothing elements 53-54- The rectifier means 6 52-53-54 may bepcled to superpose the desired transient bias on the normal steadypositive bias (derived at 49).

In like manner, the reverse situation may be stabilized by a feedbackconnection from a secondary winding All to the space-discharge means 43,and again I show a diode rectier 55 and smoothing elements connected forappropriate transient biasing of the space-discharge means 43. Ifdesired, a variable capacitance 5S may be bridged across the bias linesto the respective space-discharge devices 43-5, for changing the timeconstant of the error-rate damping which characterized operation of thetwo described eedback circuits. Similarly, a variable resistor acr ssthe bias lines to the respective spacc-discharge devices 43-45 mayprovide a means of selectably controlling the magnitude of dampingcharacterizing the error-rate compensation.

It will be appreciated that I have described an ingenious, andstructurally relatively simple, variable-reluctance control means providg great flexibility of control for a multiple-phase load. lillyarrangements lend themselves to compact packaging, and the amount ofpower to be handled delivered may be relatively great for a given-sizepackage. The constructions may be extremely rugged and may utilize aminimum of vacuum tubes, may require a minimum ci special powersupplies, and may be .relatively inse isitive to spurious magneticshunts as occasioned by the relative proximity ci fe r -magneticmaterials other tran in the core of the device. is applied to stabilizedcontrol of a motor, my arrangcment may provide very effective error-ratedamping, with no impairment of power ratinT or of control response andsensitivity. Furthermore, the time constant and the magnitude orerror-rate damping may be readily adjust-ed to meet a desiredload-handling characteristic.

While I have described my invention in detail for the preferred formsshown, it will be understood that va 'ious changes and modications maybe made within the scope of the invention as defined in the appendedclaims.

I claim:

l. In a device of the character indicated, magnetic-core means compising two closed fluxloop paths, primary-winding means including twoseparate primary windings respectively coupled to each of said paths forcirculating huizes independently in said paths when said 1 winding meansis energized, secondar" -w nding means including two separate secondarywindings respectiveiy coupled to each of paths and differentiallyconnected, whereby a load connected to said secondary-winding means maybe excited in accordance with the instantaneous diilerence in fluxescirculating in said paths, tertiary-winding means including two separatetei'- tiary windings respectively coupled to each of paths, and controlmeans including impedance-s respectively connected to each of saidtertiary windings, one of said impedances being variable, whereby therelative flux in said paths may be selectively varied while the total insaid paths remains substantially constant, and also while said coremeans remains unsat, rated.

2. A device according to claim l, in which said uX-loop paths aremagnetically independent of each other.

3. A device according to claim l, in which said ux loop paths each havea common portion constituting a common leg of said core means.

4. In a device of the character indicated, magnetic-core meanscomprising two ux-loop paths, primary-winding means coupled to each cisaid paths for circulating fluxes in said paths when saidprimary-winding means is energized, secondary-winding means coupledindependently to said paths and dierentially connected, control meansincluding a variable impedance and a tertiary winding coupled to one ofsaid paths, and auxiliary-winding means independently coupled to each ofsaid paths and connected in series, whereby for a given energizing ofsaid primary-winding means the output of said auxiliary-winding meansmay be substantiallyfconstant regardless of variations in the relativemagnitudes oi iiuxes circulating in said paths as affected by operationof said control means.

5. In a device of the character indicated, a three-legged transformercore conip-ising two outer legs and a central leg, primary-winding meanscoupled to said outer legs, second-winding means coupled to said outerlegs, and tertiarywinding means coupled to said outer legs, saidprimary-winding means being interconnected to produce fluxes flowing inthe same direction in said center leg when said primary-winding means isenergized, said secondary-winding means being differentially connected,and control means including a variable impedance connected to one ofsaid tertiary windings.

6. in a device of the character indicated, a three-legged transformer'core dening essentially two flux-loop paths with a common leg,primary-winding means coupled independently to each of said pathsexternally of said common leg, secondary-winding means coupledindependently to said paths externally of said common leg, andtertiary-winding means coupled to one of said paths externally of saidcommon leg, whereby shunt magnetic paths may be ineiective to disturbiiux linlrages in said paths.

7. A device according to claim 6, in which said primary-winding meanscomprises an equal number of turns coupled to each of said paths.

8. A device according to claim 6, in which said secondary-winding meanscomprises an equal number of turns coupled to each of said paths.

9. n a device of the character indicated, magnetic-core means comprisingtwo flux-loop paths, two like primary windings independently coupled toeach of said paths, two like secondary windings independently coupled toeach of said paths, said secondary windings being connected to eachother in a sense opposed to the interconnection of said primarywindings, and said primary windings being interconnected independentlyof said secondary windings, whereby upon energizing said primarywindings said secondary windings may present differentially opposedoutputs, and variable-reluctance means coupled to one of said paths forderiving in the combined outputs of said secondary windings a signal ofmagnitude and phase reflecting a control operation of saidvariable-reluctance means.

10. A device according to claim 9, in which two like auxiliary windingsare coupled independently to said. paths and are interconnected in thesame sense as said primary windings are interconnected, whereby theoutput voltage oi said auxiliary windings may be substantially constantfor a given energizing of said primary windings, more or less regardlessof control operations of said variable-reluctance means.

11. In a device of the character indicated, magnetic-core meanscomprising two flux-loop paths, primary-winding means or directconnection to a source of alternating current independently coupled toeach of said paths for circulating fluxes independently in said pathswhen said primary winding means is energized, secondary-winding meansindependently coupled to said paths, said primary-Winding means beingcoupled to said paths in a sense opposed to the coupling of saidsecondary-winding means to said paths, whereby the outputs of saidsecondary-winding means may reflect the differential combination ofiiuxes circulating in said paths, two tertiary windings eachindependently connected to one of said paths, control means including avariable impedance connected to one of said tertiary windings forcontrolling the ilow of llux in a iirst path as compared with the ilowof flux in the second path, and control-stabilizing means responsive toa coupling to said second path and connected to said control means in asense opposed to the operation or" said control means, whereby in anoperation of said control means to reduce the ilow of flux in said rstpath, with resulting increase in the now of ilus; in said second path,said stabilizing means may respond to the increased flow of flux in saidsecond path to oset or reduce the controlling operation of said controlmeans.

12. A device according to claim 11, in which said stabilizing meansincludes a rectifier connected to bias said control means.

13. A device according to claim 12, in which said rectifier includessmoothing means.

14. A device according to claim 11, in which said control means includesa space-discharge device and in which said stabilizing means isconnected in biasing relation with said space-disa charge device.

15. In a device of the character indicated, magnetic-control meanscomprising two flux-loop paths, primary-winding means independentlycoupled to each of said paths for circulating ilux independently in saidpaths when said primarywinding means is energized, secondary-windingmeans coupled independently to said paths, said primary-winding meansand said secondarywinding means being coupled to said paths in opposedsenses, whereby the output of said secondary-winding means may reflect adifferential combination of the fluxes in said paths, a tertiary windingcoupled to each or said paths, control means including a space-dischargedevice in controlling relation with each of said tertiary windings, rstbiasing means responsive to coupling with one of said paths andconnected to bias the space-discharge device associated with the otherof said paths with increasing force upon an increased flow of flux insaid one path, second biasing means responsive toa coupling with theother ot said paths and connected to bias the space-discharge deviceassociated with the one oi said paths with increasing force upon anincreased flow of flux in said other path.

16. A device according to claim 15, in which said biasing means areinterconnected by a variable impedance, whereby the damping function oisaid biasing means may be adjustably controlled.

i7. A device according to claim 16, in which said variable impedance isa variable capacitor, whereby the time constant of error-rate dampingmay be adjustably selected.

18. A device according to claim 16, in which said impedance is avariable resistor, whereby the magnitude of error-rate damping may beadjustably selected.

19. In a device of the character indicated, magnetic-core meanscomprising two flux-loop paths, two like separate primary windingsindependently coupled to said paths, two like separate secondarywindings independently coupled to said paths, two like separate tertiarywindings independently coupled to said paths, said primary windings being interconected in a sense opposed to said secondary windings, rstspace-discharge means connected in push-pull to a rst tertiary winding,second space-discharge means connected in push-pull to the secondtertiary winding, means interconnecting the inputs to said push-pullspace-discharge devices in a phased relation effecting a flux control inone path of phase opposite to that of the flux control in the other pathupon application of a given input signal, Xed biasing means for saidspace-discharge means and connected to bias said space-discharge meansbelow cut-oil` in the absence of a signal input, rst variable biasingmeans responsive to an increased flow of flux in one path and connectedin further biasing relation with the space discharge means for saidother path, and second variable biasing means responsive to an increasedow of flux in the other path and connected in further biasing relationwith the space-discharge means for said one path.

20. In a device of the character indicated, magnetic-core meansincluding two flux-loop paths magnetically independent of each other forat least a portion of each of said paths, primary, secondary, andtertiary coils coupled to the independent portions of said paths, meansinter- 10 connecting said primary coils in a sense opposed tointerconnection of said secondary coils, and control means including avariable impedance connected to one of said tertiary coils.

21. In a device of the character indicated, magnetic-core meansincluding two flux-loop paths magnetically independent of each other forat least a portion of each of said paths, primary, secondary, andtertiary coils coupled in mutual adjacency to the independent portionsof said paths, means interconnecting said primary coils in a senseopposed to interconnection of said secondary coils, and control meansincluding a variable impedance connected to one of said tertiary coils.

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